P0135 on the 2021 Honda HR-V
The 2021 Honda HR-V (2nd generation) uses a 1.8L naturally aspirated four-cylinder engine (R18ZC, 141 hp) with a CVT transmission. The P0135 code indicates the upstream O2 sensor heater circuit has malfunctioned. As an inline four-cylinder, there is only one bank, and the sensor sits on the exhaust manifold before the catalytic converter. The naturally aspirated 1.8L has a simpler exhaust layout than turbocharged Hondas, making diagnosis and repair straightforward.
Understanding the HR-V's O2 Heater System
The HR-V's small 1.8L engine produces moderate exhaust temperatures compared to Honda's turbocharged lineup. The O2 sensor heater is essential because the smaller engine generates less exhaust heat, meaning the sensor would take longer to warm up without the heater, especially in cold weather. The heater brings the sensor to operating temperature in about 20-30 seconds, which is critical for emissions compliance during cold starts.
Common Causes
- Heater element burnout: At 3-5 years old with potentially 30,000-70,000 miles, the 2021 HR-V can experience heater failure, especially if used primarily for short urban trips with frequent cold starts. The 1.8L naturally aspirated engine is gentler on sensors than turbo engines, but the heater element still degrades from thermal cycling.
- Blown heater fuse: The HR-V's underhood fuse box has a dedicated fuse for the O2 sensor heater circuit. This is always the first thing to check, as it is the cheapest and simplest fix.
- Connector corrosion: The HR-V's compact size means the sensor connector is positioned close to the road surface where it is exposed to water, salt, and debris. Corroded pins can disrupt the heater circuit.
- Wiring fault: The heater circuit wiring on the HR-V is relatively short and well-protected, but heat exposure near the exhaust manifold or physical damage from road debris can cause shorts or opens.
Symptoms
The check engine light will illuminate. On the HR-V's small engine, the extended warmup period from a failed heater may be more noticeable than on larger engines. Cold-start idle may be rougher, and the engine may feel slightly sluggish for the first couple of minutes. Fuel economy on short trips can decrease from the typical 28-34 MPG range. Once warm, everything returns to normal.
Diagnosis Steps
- Check the O2 heater fuse in the underhood fuse box.
- Disconnect the sensor and measure heater resistance: 2-15 ohms is healthy, open circuit means the heater is burned out.
- Verify 12V power supply at the heater circuit pins with key on.
- Inspect the sensor connector for corrosion and water damage.
- If the heater resistance is open, replace the entire sensor (heater is not separately serviceable).
Repair Costs
The HR-V is one of Honda's most affordable vehicles to repair. OEM Denso sensor: $70-$140. Aftermarket: $30-$70. Dealer labor: $80-$150. Total dealer: $150-$290. Independent shops: $100-$200. DIY: $30-$140 for the sensor. Fuse: under $10. The 2021 HR-V should still be within the federal emissions warranty (8 years/80,000 miles).
DIY Guide
The upstream O2 sensor on the HR-V 1.8L is one of the most accessible in the Honda lineup. The naturally aspirated engine has no turbo plumbing to navigate around. The sensor is clearly visible from above the engine bay. Use a 22mm O2 sensor socket. Apply penetrating oil if the sensor has been in place for a few years. The entire job takes 15-30 minutes, making it one of the easiest DIY repairs on this vehicle. Always check the fuse first.